1. Field of the Invention
The present invention relates to a work vehicle such as a tractor, and more specifically relates to a work vehicle having a loader provided in a front or rear part of a vehicle body thereof.
2. Description of the Background Art
In a known structure, in a loader mounted to a work vehicle such as a tractor, a pair of left and right booms are moved up and down by a cylinder or a link mechanism, and a scooping action and a dumping action are performed by using a bucket or the like arranged at distal ends of the booms (for example, see Japanese Patent Application Laid-Open No. 2010-185246).
In the tractor and the like, instead of the bucket, an implement having an oil hydraulic cylinder may be attached to the distal end of the booms. Known examples of the implement include a roll grab, a grapple, a bucket with grapple, and a bucket having an openable bottom. The roll grab has a pair of left and right arms openable and closable in a left-and-right direction. An oil hydraulic cylinder provided in the roll grab for an opening and closing operation is extended and retracted, and thereby the arms are opened and closed in the left-and-right direction to perform a gripping action for gripping a roll bale or the like. The grapple has a pair of comb-like arms openable and closable in an up-and-down direction. An oil hydraulic cylinder provided in the grapple for an opening and closing operation is extended and retracted, and thereby the arms are opened and closed in the up-and-down direction to perform a gripping action for gripping a fallen tree or the like. The bucket with grapple has a comb-like grapple movable in the up-and-down direction being provided above a normal bucket. An oil hydraulic cylinder provided in the bucket is extended and retracted, and thereby a gripping action is performed for gripping a fallen tree or the like with the bucket and the grapple. In the bucket having the openable bottom, an oil hydraulic cylinder provided in the bucket is extended and retracted, and thereby a bottom surface is opened to discharge soil out of the bucket.
The above-mentioned work vehicle sometimes adopts a structure in which the flow rate of an operating oil supplied in order to move the cylinder to one side can be increased by a predetermined operation. In such a structure, in a case where a bucket is mounted to the booms, a dumping action of the bucket can be performed at a higher speed as compared with the scooping action, thus achieving an improved operation efficiency. However, in this structure, in a case where an implement (such as the roll grab) including an oil hydraulic cylinder is attached, only one of extension and retraction of the cylinder of the implement is performed at a high speed. For example, in a case where the roll grab or the grapple is attached, only one of an opening operation and a closing operation of the arms can be performed at an increased speed. This may confuse an operator.